High efficiency optical devices

Abstract

Optical devices such as backlight assemblies, according to the present invention include a multilayer optical film in which at least one of the layers comprises an oriented birefringent polymer. The multilayer optical film exhibits low absorptivity and can reflect light approaching at shallow angles as well as normal to the film.

What is claimed is: 
     
       1. A backlight assembly, comprising:
 a light guide comprising opposing optical surfaces, wherein at least a portion of the opposing optical surfaces comprises a multilayer optical film that comprises alternating layers of at least two materials, wherein the multilayer optical film reflects light over a wavelength band of interest as a function of thicknesses of the alternating layers, wherein at least one of the materials has a stress induced birefringence, and further wherein at least one opposing optical surface comprises a plurality of voids formed in the multilayer optical film; and 
 at least one light source positioned between the opposing optical surfaces, wherein at least one void of the plurality of voids is capable of transmitting light emitted by the at least one light source. 
 
     
     
       2. The assembly of  claim 1 , wherein the multilayer optical film comprises a mirror. 
     
     
       3. The assembly of  claim 1 , wherein at least one void of the plurality of voids comprises a physical aperture. 
     
     
       4. The assembly of  claim 1 , wherein at least one void of the plurality of voids comprises a transparent area. 
     
     
       5. The assembly of  claim 1 , wherein the multilayer optical film comprises alternating first and second polymeric materials, wherein the first polymeric material is birefringent and the second polymeric material is isotropic. 
     
     
       6. The assembly of  claim 1 , wherein the light guide is hollow. 
     
     
       7. The assembly of  claim 1 , wherein the multilayer optical film comprises alternating first and second polymeric materials, wherein the absolute value of the difference in index of refraction between the first and second polymeric materials is Δnx along an in-plane direction of the film and is Δnz along a thickness direction of the film, and wherein Δnx is at least 0.05 and Δnz is less than Δnx. 
     
     
       8. The assembly of  claim 1 , wherein the multilayer optical film is laminated to a support. 
     
     
       9. The assembly of  claim 1 , wherein the plurality of voids are uniformly distributed in the opposing optical surface. 
     
     
       10. The assembly of  claim 1 , wherein the plurality of voids are randomly distributed in the opposing optical surface. 
     
     
       11. The assembly of  claim 1 , wherein each void of the plurality of voids is of equal size. 
     
     
       12. A backlight assembly, comprising:
 a light guide comprising opposing optical surfaces and an opening substantially orthogonal to the opposing optical surfaces, wherein at least a portion of the opposing optical surfaces comprises a multilayer optical film that comprises alternating layers of at least two materials, wherein the multilayer optical film reflects light over a wavelength band of interest as a function of thicknesses of the alternating layers, wherein at least one of the materials has a stress induced birefringence, and further wherein at least one opposing optical surface comprises a plurality of voids formed in the multilayer optical film; and 
 at least one light source positioned proximate the opening, wherein at least one void of the plurality of voids is capable of transmitting light emitted by the at least one light source. 
 
     
     
       13. The assembly of  claim 12 , wherein the multilayer optical film comprises a mirror. 
     
     
       14. The assembly of  claim 12 , wherein at least one void of the plurality of voids comprises a physical aperture. 
     
     
       15. The assembly of  claim 12 , wherein at least one void of the plurality of voids comprises a transparent area. 
     
     
       16. The assembly of  claim 12 , wherein the opposing optical surfaces converge towards each other as the distance from the opening into the light guide increases. 
     
     
       17. The assembly of  claim 12 , wherein the multilayer optical film comprises alternating first and second polymeric materials, wherein the first polymeric material is birefringent and the second polymeric material is isotropic. 
     
     
       18. The assembly of  claim 12 , wherein the light guide is hollow. 
     
     
       19. The assembly of  claim 12 , wherein the multilayer optical film comprises alternating first and second polymeric materials, wherein the absolute value of the difference in index of refraction between the first and second polymeric materials is Δnx along an in-plane direction of the film and is Δnz along a thickness direction of the film, and wherein Δnx is at least 0.05 and Δnz is less than Δnx.